The present disclosure relates to an optical fiber laser device.
Optical fiber laser devices using an optical fiber for an optical amplifying portion of a laser oscillator or an optical amplifier have been used in various fields such as laser-processing or the like.
In such optical fiber laser devices, a so-called return light problem occurs sometimes that a reflected laser light is coupled to a core of an optical fiber inside the optical fiber laser device (for example, see WO2014/014068 or WO2012/073952). When the optical fiber laser device is used as a laser-processing apparatus, this return light is generated because, for example, laser light irradiated to a workpiece is reflected by the workpiece. This return light is considered to be generated by a reflection as well at various locations such as a crack in the optical fiber used in the optical fiber laser device, a defect at an optical connection portion.
This return light may be propagated in the optical fiber in the optical fiber laser device in a reverse direction of laser light output by the laser oscillator, and it may damage composing parts of the optical fiber laser device sometimes. A composing part of the optical fiber laser device which may be affected and damaged by the return light may be, for example, a light emission element that emits a guide light pointing a position where laser light for laser machining is emitted. Even if a composing part is not provided to an end portion where the return light reaches, it may be a problem from a view point of securing safety if high power return light is emitted from the end portion.
However, the above-described return light may be unforeseeable qualitatively and quantitatively sometimes. For example, the return light may be amplified while propagating through an oscillator or an amplifier in the optical fiber laser device. A stimulated Raman scattered light whose wavelength is longer than that of laser light oscillated by the laser oscillator may be generated sometimes in a process of propagation through the optical fiber in the optical fiber laser device. Therefore, when adopting a countermeasure for return light with specific power and specific wavelength, the return light could not be attenuated appropriately, and thus, composing parts of the optical fiber laser device may be damaged.